The present invention relates generally to scroll-type machines. More particularly, the present invention relates to hermetic scroll compressors incorporating a fluid injection system where the fluid injection system injects the fluid into the suction line of the compressor when a temperature limit is exceeded.
Refrigeration and air conditioning systems generally include a compressor, a condenser, an expansion valve or an equivalent and an evaporator. These components are coupled in sequence in a continuous flow path. A working fluid flows through the system and alternates between a liquid phase and a vapor or gaseous phase.
A variety of compressor types have been used in refrigeration systems, including but not limited to reciprocating compressors, screw compressors and rotary compressors. Rotary type compressors can include the various vane type compressors as well as scroll machines. Scroll machines or scroll compressors are constructed using two scroll members with each scroll member having an end plate and a spiral wrap. The scroll members are mounted so that they may engage in relative orbiting motion with respect to each other. During this orbiting movement, the spiral wraps define a successive series of enclosed spaces or crescent shaped pockets, each of which progressively decrease in size as it moves inwardly from a radial outer position at a relatively low suction pressure to a central position at a relatively high discharge pressure. The compressed gas exits from the enclosed space at the central position through a discharge passage formed through the end plate of one of the scroll members.
In the normal refrigeration cycle, vapor is drawn into a compressor where it is compressed to a higher pressure. The compressed vapor is cooled and condensed in a condenser into a high pressure liquid which is then expanded, typically through an expansion valve, to a lower pressure and caused to evaporate in an evaporator to thereby draw in heat and thus provide the desired cooling effect. The expanded, relatively low pressure vapor exiting the evaporator is once again drawn into the compressor and the cycle starts anew. The action of compressing the lower pressure vapor imparts work onto the higher pressure vapor and results in a significant increase in the vapor temperature. While a substantial portion of this heat caused by the compression process and the evaporating process is subsequently rejected to the atmosphere during the condensation process, a portion of the heat is transferred to the compressor components. Depending upon the specific refrigerant vapor compressed and on the pressure conditions of operation, this heat transfer can cause the temperature of the compressor components to rise to levels which may cause the compressor to overheat, resulting in degradation of the compressor""s performance and lubrication and possible damage to the compressor.
In order to overcome overheating problems, various methods have been developed for injecting gaseous or liquid refrigerant under pressure into the closed pockets of the scroll compressor. One known prior art method of injecting the liquid refrigerant from the refrigerant cycle into the enclosed pockets is to inject the liquid refrigerant using an injection fitting which has an opening which is positioned in alignment with a suction inlet defined by one of the scroll members. The injected liquid is sucked into the closed pockets to cool the compressed gas. This method is described in Assignee""s U.S. Pat. No. 5,076,067; the disclosure of which is incorporated herein by reference. Another known prior art method of liquid injection is to injert the liquid refrigerant from the refrigeration cycle directly into one or more of the closed pockets through an intermediate pressurized biasing chamber which is in communication with one or more of the closed pockets. The injected liquid cools the compressed gas in the closed pockets. This method is described in Assignee""s U.S. Pat. Nos. 5,329,788 and 5,447,420; the disclosures of which are incorporated herein by reference. Another known prior art method of liquid injection is to inject the liquid refrigerant from the refrigeration cycle directly into one or more of the closed pockets through a passage extending through one of the scroll members and opening into one or more of the closed pockets at a position which is as close as possible to the central portion of the scroll member or as close as possible to the actual discharge. This method is described in Assignee""s U.S. Pat. No. 5,469,816; the disclosure of which is incorporated herein by reference.
Each of these prior art systems offer advantages and disadvantages even though they perform successfully in the refrigeration compressors. The injection into the suction inlet of the scroll members offers simplicity but it also requires an additional fitting which extends through the hermetic shell. The systems that inject directly into one or more of the closed pockets are able to more accurately control the temperature but they require additional machining of the scroll members as well as requiring an additional fitting which extends through the hermetic shell of the scroll compressor.
The present invention overcomes these disadvantages by providing a simple yet effective method for injecting liquid refrigerant into the pockets formed by the scroll members to reduce the temperature of the compressed gas. The present invention uses a temperature sensing device on the top cap of the hermetic shell to sense the temperature of the discharge gas. When the discharge gas temperature exceeds a specified limit, an electronic control will open a device to inject a certain quantity of liquid refrigerant into the suction line of the scroll compressor. The injecting device can be an electronic expansion valve, a pulsing (pulse width modulator) valve or any other known method of having a controllable opening of a fluid passage. The method of the present invention provides an effective low cost liquid injection system which only requires simple modifications of the scroll compressor and the refrigeration system.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.